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Monarch caterpillars are vulnerable to neonicotinoid toxicity at concentrations as low as 1 part per billion, writes Jonathan Latham, and that makes them vulnerable to residues from commercial crops - and even more so from horticultural use in plant nurseries!

USDA researchers have identified the neonicotinoid insecticide clothianidin as a likely contributor to monarch butterfly declines in North America.

The USDA research is published in the journal Science of Nature and was published online on 3rd April (Pecenka and Lundgren 2015).

Monarch butterfly populations (Danaus Plexippus) have declined precipitously in North America in the last twenty years. This decline has commonly been linked to loss of milkweeds (Asclepias species) from farmer's fields.

Monarch caterpillars are dependent on milkweeds. The ability of farmers to kill them with the Monsanto herbicide Roundup (glyphosate) has therefore led to this herbicide being considered as a major contributor to the decline of the monarch butterfly.

However, industrial farming methods include other known or potential causes of monarch disappearances. One of these is the known toxicity of Bt insecticides found in GMO crops.

For instance, in 2006 pollen from Syngenta's BT176 corn (no longer on the US market) was shown to have a lethal dose of 14 pollen grains towards caterpillars of European Swallowtail butterflies.

Pollen from GMO crops falls on the milkweeds where monarchs feed and individual maize plants produce millions of pollen grains.

'Neonic' pesticides - toxic to caterpillars at 1 part per billion

Neonicotinoids have been strongly implicated in pollinator declines worldwide, as shown by a report from a task force of the International Union of Nature Conservation based in Switzerland.

These pesticides, such as clothianidin (Bayer), are a particular hazard because, unlike most pesticides, they are water-soluble molecules.

From soil or seed treatments they can reach nectar and are found in pollen. They are now the most widely used pesticides in the world (Goulson 2013). Up to now there has been negligible research on the effects of neonicotinoids on butterflies and this new research is therefore the first to link neonicotinoids to the survival and reproduction of any butterfly.